1. Field of the Invention
The present invention relates to a transmission system for performing optical spatial transmission or optical bus transmission in an arrangement for office automation or local area networks, and other kinds of equipment.
2. Description of the Prior Art
The inventors of the present invention have proposed before a data transmission device in Japanese Patent Application SHO 61-165830, wherein, as shown in FIG. 15, a controller 61, used as a master station, is connected to slave stations 62 which are input/output units to a sensor or an actuator via an optical fiber or the like in a manner to assume a loop.
On the other hand, Japanese Laid-open Patent Publication SHO 59-95746 has disclosed an arrangement for spatial optical transmission. The arrangement not only enables bilateral transmission, but realizes transmission of one-to-many signals between the home and slave stations in a wide area, with considerations given to interference between many communication stations. As shown in FIG. 16, according to the disclosed arrangement, a plurality of non-directive optical transceivers 66 are connected to a ceiling 65 or a wall in the station yard, etc. via a wire cable 67. Each terminal device is provided with a directive optical transceiver 68 which is communicable with one of the non-directive optical transceivers 66, so that the transmission data added to an address data of the subject party is transmitted to the non-directive optical transceiver 66 from the directive optical transceiver 68. The data is then transmitted from all of the non-directive optical transceivers 66 to the corresponding directive optical transceivers 68. Each terminal device identifies the address data contained in the transmission data so as to thereby read the transmission data.
In the former arrangement, namely, in a loop optical transmission device having a master station 61 and slave stations 62 directly connected in series by means of one optical transmission path 63, wiring of an optical fiber or the like is not avoidable, and therefore it causes an increase of costs if the layout should be changed frequently or the arrangement cannot be employed at all if the circumstances can not afford the use of optical fiber. Moreover, the usage of the optical fiber is limited in a movable part, etc. in order to prevent the deterioration of the optical fiber.
According to the latter method revealed in Japanese Laid-open Patent Publication SHO 59-95746, since spatial optical transmission is applied to the method, the above-described disadvantages are not brought about. However, it takes a lot of time to adjust for the collision of data, thereby losing accessibility of data in real time. Further, a complete wiring-free arrangement is difficult because of the necessity of a cable.